This invention relates to a semi-submersible vessel used in connection with offshore operations, services and resource exploration. More particularly, this invention relates to a hybrid of a column stabilized semi-submersible vessel which expands the useful operations and life thereof.
Increased energy demands and decreased energy resources have created a need to explore and produce resources from deeper offshore areas. The demands of deep water exploration and installation present many technical problems for vessel designers. Existing technology used in offshore operations, services and resource exploration fails to adequately address the many challenges associated with deep water.
Placement of equipment in deep waters necessitates new methods of installation, maintenance, repair and removal. For example, rapid transit speed combined with installation and removal capabilities are desired features which are inadequate in existing designs. Service and maintenance needs related to equipment placed in extreme depths, e.g., flow lines, jumpers, tie-ins and service umbilicles, presents significant issues which known technology fails to adequately address. The time frames associated with installation, maintenance, repair and removal services precludes the use of mooring systems in deep water. Thus, efficient station keeping techniques are required.
One type of vessel used in deep waters is known as a semi-submersible vessel. A semi-submersible vessel comprises a deck section which is typically supported by four or more vertical columns which rest on two or more pontoons. The pontoons and portions of the columns are submerged below the operational water line during normal operation. In order to provide adequate structural integrity, cross brace support members are typically used between the columns. Cross brace support members, while essential to the structural integrity of traditional designs for semi-submersible vessels, create undesirable characteristics. For example, cross brace support members create hydrodynamic drag and create problems related to underslung loads.
U.S. Pat. No. 4,436,050 illustrates a hybrid of a traditional cross braced semi-submersible vessel. In the disclosed vessel, a pair of support members run generally parallel between the pontoons. Such an alternative design fails to fully address performance and operational issues.
Canadian Patent No. 1,279,531 discloses a semi-submersible vessel without any cross bracing, but fails to disclose means which would adequately support such a structure.
Thus, a need remains for an improved semi-submersible vessel design with expanded capabilities, and alternative structural supports which do not unnecessarily interfere with advantageous operations of such vessels.